The present invention relates to an apparatus for inspection of concave elements, such as containers, caps or like.
More specifically, the invention concerns an apparatus for checking concave elements, and particularly plastic caps, for closing bottles containing soft drinks or like, that can inspect concave surface permitting detection of contaminations and/or defects, such as material exceeding and/or lacking, shape and/or assembling defects.
In the following, the specification will be addressed to the inspection of plastic caps for soft drinks, but it is well evident that the same must not be considered limited to this specific use.
As it is well known, plastic bottles (PET and like) are always more used, said bottles having high hygiene standards and highly reducing transportation expenses, mainly for their reduced weight. Plastic bottles are sealed by suitable caps, coupled by threading. Furthermore, different caps are used on the basis of the beverage contained within the bottle. For carbonated beverages, they are employed caps providing disc-shaped gaskets on the bottom of concave surface, also known as “liners”, suitable to limit exit of gas from the bottle. Edge of said gasket is inserted between the cap bottom and a circular relief obtained on the inner lateral surface of the cap, overlapping on said gasket. Instead, caps are used for not carbonated beverages provided with a sealing ring, interacting with the bottle edge.
In this field it is felt the needing of controlling the positioning of the gasket or of the proper shape of the sealing ring, necessary both for ensuring a proper preservation of the product contained within the bottle, and for preventing that beverage can leak additive gas, mainly from the gasket.
At present, different systems exist permitting detecting caps defects, mainly optical systems. Among these solutions it is possible mentioning those described in EP 1078228 B1, JP 9068503, EP 0371547 and JP 2004109064 A, which substantially comprise a camera or sensor, means for lighting the cap to be inspected, an optical group suitable to transmit cap images detected to the camera or sensor lens, so as to obtain an optical representation of said cap. Furthermore, usually, known apparatuses have means for processing images, for automatically detecting cap defects.
However, known systems do not solve the problem of detecting proper positioning of the gasket. Further, optical group used in known apparatuses cannot analyse inner structure of caps, often very complicated.
Finally, due to the always more strict marketing needings, beverage bottles, as well as relevant caps, have different colours. This make difficult maintaining a high reliability level in detecting defects, since contrast between the same cap and the gasket is too low.